1. Field of Invention
The present invention provides sustained-release formulations of a pharmacologically active ingredient or ingredients, especially of ones which have been hardly formulated because of their high solubility in water (hereinafter sometimes referred to as water-soluble active ingredients), and methods for preparing sustained-release formulations of them are also provided.
2. Prior Arts
A number of reports have been published on the technologies for effectively controlling dissolution and absorption of water-soluble pharmacologically active ingredients, especially of active ingredients which are very soluble in gastric or intestinal juice.
These technologies for sustainment of drugs may be classified generally into two types. One is achieved by forming matirix and the other is by film-coating.
For example, the sustained-release has been accomplished by granulating an active ingredient together with a hydrophobic substance to form matrices as disclosed in Japanese Patent Publication No. 60-56122. However, there is no disclosure on the release-control over four hours in the publication above.
In JPN Patent Application No. 61-1614, the sustained-release has been accomplished by making triple layers with three different types of pH-dependent film-coating materials. In the above process, however, troublesome coating steps are required and moreover a large amount of coating materials must be employed for the limited amount of the active component in order to achieve appropriate sustained-release. Moreover, the use of such a large amount of coating materials unfavourably decreases bio-availability of the active ingredients.